Ferroelectric memory cell sensing

ABSTRACT

Methods, systems, and devices for operating a ferroelectric memory cell or cells are described. A memory device may maintain a digit line voltage at a ground reference for a duration associated with biasing a ferroelectric capacitor of a memory cell. For example, a digit line that is in electronic communication with a ferroelectric capacitor may be virtually grounded while a voltage is applied to a plate of the ferroelectric capacitor, and the ferroelectric capacitor may be isolated from the virtual ground after a threshold associated with applying the voltage to the plate is reached. A switching component (e.g., a transistor) that is in electronic communication with the digit line and virtual ground may be activated to virtually ground the digit line and deactivated to isolate the digit line from virtual ground.

CROSS REFERENCE

The present application for patent is a continuation of U.S. patentapplication Ser. No. 16/059,727 by Kawamura et al., entitled“Ferroelectric Memory Cell Sensing,” filed Aug. 9, 2018, which is acontinuation of U.S. patent application Ser. No. 15/690,873 by Kawamuraet al., entitled “Ferroelectric Memory Cell Sensing,” filed Aug. 30,2017, which is a continuation of U.S. patent application Ser. No.15/073,989 by Kawamura et al., entitled “Ferroelectric Memory CellSensing,” filed Mar. 18, 2016, each of which is assigned to the assigneehereof, and each of which is expressly incorporated by reference in itsentirety herein.

BACKGROUND

The following relates generally to memory devices and more specificallyto increasing a sensing scheme for a ferroelectric memory cell.

Memory devices are widely used to store information in variouselectronic devices such as computers, wireless communication devices,cameras, digital displays, and the like. Information is stored byprogramming different states of a memory device. For example, binarydevices have two states, often denoted by a logic “1” or a logic “0.” Inother systems, more than two states may be stored. To access the storedinformation, the electronic device may read, or sense, the stored statein the memory device. To store information, the electronic device maywrite, or program, the state in the memory device.

Various types of memory devices exist, including random access memory(RAM), read only memory (ROM), dynamic RAM (DRAM), synchronous dynamicRAM (SDRAM), ferroelectric RAM (FeRAM), magnetic RAM (MRAM), resistiveRAM (RRAM), flash memory, and others. Memory devices may be volatile ornon-volatile. Non-volatile memory (e.g., flash memory) can store datafor extended periods of time even in the absence of an external powersource. Volatile memory devices (e.g., DRAM) may lose their stored stateover time unless they are periodically refreshed by an external powersource. A binary memory device may be an example of a volatile memorydevice and may store a logic state by charging or discharging acapacitor. A charged capacitor, however, may become discharged over timethrough leakage currents, resulting in the loss of the storedinformation. Certain features of volatile memory may offer performanceadvantages, such as faster read or write speeds, while features ofnon-volatile memory, such as the ability to store data without periodicrefreshing, may be advantageous.

FeRAM may use similar device architectures as volatile memory but mayhave non-volatile properties due to the use of a ferroelectric capacitoras a storage device. FeRAM devices may thus have improved performancecompared to other non-volatile and volatile memory devices. In order todetermine a logic state stored by a ferroelectric memory cell, a cellplate of the ferroelectric memory cell may be biased to some voltage.Biasing the cell plate, however, may result in undesired behavior inneighboring circuit locations—e.g., a parasitic voltage may be inducedon a digit line—due to parasitic elements or material properties withinthe memory device.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure herein refers to and includes the following figures:

FIG. 1 illustrates an example memory array that supports a sensingscheme for a ferroelectric memory cell in accordance with variousembodiments of the present disclosure;

FIG. 2 illustrates an example circuit that supports a sensing scheme fora ferroelectric memory cell in accordance with various embodiments ofthe present disclosure;

FIG. 3 illustrates example hysteresis plots for operating aferroelectric memory cell in accordance with various embodiments of thepresent disclosure;

FIG. 4 illustrates an example circuit that supports a sensing scheme fora ferroelectric memory cell in accordance with various embodiments ofthe present disclosure;

FIG. 5 illustrates a timing diagram for a sensing scheme for aferroelectric memory cell in accordance with various embodiments of thepresent disclosure;

FIG. 6 illustrates an example ferroelectric memory array that supports asensing scheme for a ferroelectric memory cell in accordance withvarious embodiments of the present disclosure;

FIG. 7 illustrates a device, including a memory array, that supports asensing scheme for a ferroelectric memory cell in accordance withvarious embodiments of the present disclosure; and

FIGS. 8 and 9 are flowcharts that illustrate a method or methods for asensing scheme for a ferroelectric memory cell in accordance withvarious embodiments of the present disclosure.

DETAILED DESCRIPTION

A memory device may maintain a voltage of a digit line at a groundreference (e.g., virtual ground) for a duration associated with biasinga cell plate of a ferroelectric capacitor to combat parasitic effects,such as an induced voltage on the digit line. In one example, aswitching component may be activated to connect a digit line that is inelectronic communication with a ferroelectric memory cell to virtualground. Subsequently, a read voltage may be applied to a plate of aferroelectric capacitor of the ferroelectric memory cell to bias theferroelectric capacitor. The applied read voltage may generate parasiticeffects throughout the memory device—e.g., a voltage may be inducedvoltage on a digit line. The induced voltage on the digit line mayreduce the amount of charge that is transferred or “dumped” onto thedigit line from the ferroelectric capacitor during a read operation and,in turn, may decrease the resulting digit line voltage. So the switchingcomponent may be maintained in an active mode to continue the digitline's connection to the ground reference while the read voltage isapplied.

By maintaining the connection to the ground reference, the inducedparasitic voltage on the digit line may be dampened or driven back tothe ground reference during and after “moving” the plate voltage (i.e.,after biasing the plate). During or following the application of theread voltage, the ferroelectric memory device may deactivate theswitching component, isolating the digit line from the ground reference.The ferroelectric memory cell may then be selected for a read operationby activating a selection component of the ferroelectric memory cell,and the ferroelectric capacitor may discharge on to the digit line.

The voltage of the digit line that results from discharging thecapacitor may be based on the logic state that is stored by theferroelectric capacitor and the initial voltage of the digit line. Forinstance, the voltage of the digit line resulting from a stored logicstate “1” may be greater than the voltage of the digit line resultingfrom a stored logic state “0.” In this way, the effects of parasiticelements may be reduced and the sensing window—i.e., the differencebetween the voltage resulting from a logic “1” and a logic “0”—may beincreased for a read operation. In some cases, the increased sensingwindow may also be referred to as a “full dump” window because it allowsall or most of the charge stored on the ferroelectric capacitor to betransferred to the digit line and subsequently read, which, in turn,provides for a more accurate determination of the logic state of thememory cell.

Features of the disclosure introduced above are further described belowin the context of a memory array. Specific examples are then describedwith reference to a circuit that supports a sensing scheme for aferroelectric memory cell. These and other features of the disclosureare further illustrated by and described with reference to apparatusdiagrams, system diagrams, and flowcharts that relate to a sensingscheme for a ferroelectric memory cell.

FIG. 1 illustrates an example memory array 100 that supports a sensingscheme for a ferroelectric memory cell in accordance with variousembodiments of the present disclosure. Memory array 100 may also bereferred to as an electronic memory apparatus. Memory array 100 includesmemory cells 105 that are programmable to store different states. Eachmemory cell 105 may be programmable to store two states, denoted as alogic “0” and a logic “1.” In some cases, memory cell 105 is configuredto store more than two logic states. A memory cell 105 may include acapacitor to store a charge representative of the programmable states;for example, a charged and uncharged capacitor may represent two logicstates, respectively. DRAM architectures may commonly use such a design,and the capacitor employed may include a dielectric material with linearelectric polarization properties. By contrast, a ferroelectric memorycell may include a capacitor that has a ferroelectric as the dielectricmaterial. Different levels of charge of a ferroelectric capacitor mayrepresent different logic states. Ferroelectric materials havenon-linear polarization properties; some details and advantages of aferroelectric memory cell 105 are discussed below.

Operations such as reading and writing may be performed on memory cells105 by activating or selecting the appropriate access line 110, whichmay also be referred to as a word line 110, and digit line 115 from WL_1to WL_N and DL_1 to DL N, respectively. Activating or selecting a wordline 110 or a digit line 115 may include applying a voltage to therespective line. In some cases, a digit line 115 may be referred to as abit line. Word lines 110 and digit lines 115 are made of conductivematerials. For example, word lines 110 and digit lines 115 may be madeof metals, such as copper, aluminum, gold, tungsten, or the like.According to the example of FIG. 1, each row of memory cells 105 areconnected to a single word line 110, and each column of memory cells 105are connected to a single digit line 115. By activating (e.g., applyinga voltage to) one of the word lines 110 and one of the digit lines 115,a single memory cell 105 may be accessed at their intersection. Theintersection of a word line 110 and digit line 115 may be referred to asan address of a memory cell.

In some architectures, the logic-storing device of a cell (e.g., acapacitor) may be electrically isolated from the digit line by aselection component. The word line 110 may be connected to and maycontrol the selection component. For example, the selection componentmay be a transistor and the word line 110 may be connected to the gateof the transistor. Activating the word line 110 results in an electricalconnection or closed circuit between the capacitor of a memory cell 105and its corresponding digit line 115. The digit line may then beaccessed to either read or write the memory cell 105. Accessing memorycells 105 may be controlled through a row decoder 120 and a columndecoder 130. In some examples, a row decoder 120 receives a row addressfrom the memory controller 140 and activates the appropriate word line110 based on the received row address. Similarly, a column decoder 130receives a column address from the memory controller 140 and activatesthe appropriate digit line 115. Thus, by activating a word line 110 anda digit line 115, memory cell 105 may be accessed. For example, thememory array 100 may access memory cell 105 by activating DL_1 and WL_3.

Upon accessing, memory cell 105 may be read, or sensed, by sensecomponent 125. For example, sense component 125 may compare a signal(e.g., a voltage) of the relevant digit line 115 to a reference signalin order to determine the stored state of the memory cell 105. If digitline 115 has a higher voltage than the reference voltage, then sensecomponent 125 may determine that the stored state in memory cell 105 wasa logic “1” and vice versa. Sense component 125 may include varioustransistors or amplifiers in order to detect and amplify a difference inthe signals, which may be referred to as latching. The detected logicstate of memory cell 105 may then be output through column decoder 130as output 135. With respect to a memory cell 105 that includes aferroelectric capacitor, reading the memory cell may includebiasing—e.g., applying a voltage to—a plate of the ferroelectriccapacitor.

The applied biasing voltage may drive the ferroelectric capacitor torelease charge on to digit line 115, and so may produce a voltage ondigit line 115. The magnitude of the produced voltage may be based atleast in part on the logic state that is stored by the ferroelectriccapacitor. In some cases, the applied biasing voltage effects componentsin other locations of memory array 100 (e.g., a nearby digit line 115).These effects may be due to parasitic elements that are inherent tomemory array 100, and some examples may include parasitic capacitance,parasitic inductance, and the like. These parasitic elements may beassociated with the physical layout of memory array 100 (e.g., tracewidths, trace locations, trace lengths, etc.) and signal properties ofthe applied voltage (e.g., signal frequency, rate of voltage change,step size, etc.).

In one example of parasitic effects, the ferroelectric capacitor ofmemory cell 105 is biased by applying a read voltage to a plate of theferroelectric capacitor. Concurrently with applying the read voltage, avoltage may be induced on a corresponding digit line 115 due to theparasitic elements. When the memory cell 105 is selected via therelevant word line 110, the ferroelectric capacitor may share the storedcharge with the corresponding digit line 115. The induced voltage may,however, effectively decrease the voltage across the ferroelectriccapacitor that results from the biasing and, in turn, the amount ofcharge released by the ferroelectric capacitor on to the digit line 115,reducing the resulting change in voltage. That is, the ferroelectriccapacitor may fail to release the full amount of stored charge to thedigit line 115. By failing to fully utilize the stored charge, thedifference in the voltages that result from a logic “0” and a logic “1”may also decrease, along with the sensing window.

Therefore, the memory array 100 may maintain a digit line 115 voltage ator near a ground reference during all or a portion of the time that aread voltage in order to combat parasitic effects that result from theapplied read voltage and this mitigate sense margin loss. In someexamples, the memory array 100 may include a switching component (e.g.,a transistor) that is in electronic communication with a digit line 115and a ground reference (e.g., virtual ground) to reduce the inducedparasitic voltage. Memory array 100 may use control signals to activateand deactivate the switching component.

A memory cell 105 may be set, or written, by activating the relevantword line 110 and digit line 115. As discussed above, activating a wordline 110 electrically connects the corresponding row of memory cells 105to their respective digit lines 115. By controlling the relevant digitline 115 while the word line 110 is activated, a memory cell 105 may bewritten—i.e., a logic value may be stored in the memory cell 105. Columndecoder 130 may accept data, for example input 135, to be written to thememory cells 105. In the case of a ferroelectric capacitor, a memorycell 105 is written by applying a voltage across the ferroelectriccapacitor. This process is discussed in more detail below.

In some memory architectures, accessing the memory cell 105 may degradeor destroy the stored logic state and re-write or refresh operations maybe performed to return the original logic state to memory cell 105. InDRAM, for example, the capacitor may be partially or completelydischarged during a sense operation, corrupting the stored logic state.So the logic state may be re-written after a sense operation.Additionally, activating a single word line 110 may result in thedischarge of all memory cells in the row; thus, several or all memorycells 105 in the row may need to be re-written.

Some memory architectures, including DRAM, may lose their stored stateover time unless they are periodically refreshed by an external powersource. For example, a charged capacitor may become discharged over timethrough leakage currents, resulting in the loss of the storedinformation. The refresh rate of these so-called volatile memory devicesmay be relatively high—e.g., tens of refresh operations per second forDRAM—which may result in significant power consumption. Withincreasingly larger memory arrays, increased power consumption mayinhibit the deployment or operation of memory arrays (e.g., powersupplies, heat generation, material limits, etc.), especially for mobiledevices that rely on a finite power source, such as a battery.Ferroelectric memory cells may, however, have beneficial properties thatmay result in improved performance relative to other memoryarchitectures. For example, because ferroelectric memory cells tend tobe less susceptible to degradation of stored charge, a memory array 100that employs ferroelectric memory cells 105 may require fewer or norefresh operations, and may thus require less power to operate.

The memory controller 140 may control the operation (e.g., read, write,re-write, refresh, etc.) of memory cells 105 through the variouscomponents, for example, row decoder 120, column decoder 130, and sensecomponent 125. Memory controller 140 may generate row and column addresssignals in order to activate the desired word line 110 and digit line115. Memory controller 140 may also generate and control various voltagepotentials used during the operation of memory array 100. In general,the amplitude, shape, or duration of an applied voltage discussed hereinmay be adjusted or varied and may be different for the variousoperations for operating memory array 100. Furthermore, one, multiple,or all memory cells 105 within memory array 100 may be accessedsimultaneously; for example, multiple or all cells of memory array 100may be accessed simultaneously during a reset operation in which allmemory cells 105, or a group of memory cells 105, are set to a singlelogic state.

In some examples, the memory controller 140 may provide an input to anamplification device that is used to apply a read voltage to the plateof a ferroelectric capacitor in a memory cell 105. In other examples,the memory controller 140 may provide an input to an amplificationdevice used to select a memory cell. The memory controller 140 may alsobe used to implement feature of the sensing scheme. For instance, thememory controller 140 may provide an input to an amplification deviceused to activate and deactivate a switching component that is inelectronic communication with a digit line and virtual ground. Thememory controller 140 may also determine a timing associated withapplying a voltage to a plate of a ferroelectric capacitor and isolatingthe digit line from virtual ground by deactivating the switchingcomponent.

FIG. 2 illustrates an example circuit 200 that supports a sensing schemefor a ferroelectric memory cell in accordance with various embodimentsof the present disclosure. Circuit 200 includes a ferroelectric memorycell 105-a, word line 110-a (which may also be referred to as accessline 110-a), digit line 115-a, and sense component 125-a, which may beexamples of a memory cell 105, word line 110, digit line 115, and sensecomponent 125, respectively, as described with reference to FIG. 1.Memory cell 105-a may include a logic storage component, such ascapacitor 205, which has a first plate and a second plate that arecapacitively coupled, the first plate may be referred to as cell plate230 and the second plate may be referred to as cell bottom 215. In someexamples, the orientation of the capacitor may be flipped withoutchanging the operation of memory cell 105-a, that is, the first platemay correspond to cell bottom 215 and the second plate may correspond tocell plate 230. In the example of FIG. 2, cell plate 230 may be accessedvia plate line 210 and cell bottom 215 may be accessed via digit line115-a. Also in the example of FIG. 2, the terminals of capacitor 205 areseparated by a ferroelectric material. As described above, variousstates may be stored by charging or discharging capacitor 205, i.e.,polarizing the ferroelectric material of capacitor 205. The total chargeneeded to polarize capacitor 205 may be referred to as the remnantpolarization (PR) value, and a voltage of capacitor 205 at which halfthe total charge of capacitor 205 is reached may be referred to as thecoercive voltage (VC).

The stored state of capacitor 205 can be read or sensed by operatingvarious elements represented in circuit 200. Capacitor 205 may be inelectronic communication with digit line 115-a. For example, capacitor205 can be isolated from the digit line 115-a when selection component220 is deactivated, and capacitor 205 can be connected to digit line115-a when selection component 220 is activated to select theferroelectric memory cell 105-a. In other words, ferroelectric memorycell 105-a may be selected using selection component 220 that is inelectronic communication with ferroelectric capacitor 205, whereferroelectric memory cell 105-a includes selection component 220 andferroelectric capacitor 205. In some cases, selection component 220 is atransistor and its operation is controlled by applying a voltage to thetransistor gate, where the voltage magnitude is greater than thethreshold magnitude of the transistor. Word line 110-a may activateselection component 220; for example, a voltage applied to word line110-a is applied to the transistor gate, connecting capacitor 205 withdigit line 115-a. In an alternative embodiment the positions ofselection component 220 and capacitor 205 may be switched, such thatselection component 220 is between plate line 210 and cell plate 230 andsuch that capacitor 205 is between digit line 115-a and the otherterminal of selection component 220. In this embodiment, selectioncomponent 220 may remain in electronic communication digit line 115-athrough capacitor 205. This configuration may be associated withalternative timing and biasing for read and write operations.

Due to the ferroelectric material between the plates of capacitor 205,and as discussed in more detail below, capacitor 205 may not dischargeupon connection to digit line 115-a. In one scheme, to sense the statethat is stored by ferroelectric capacitor 205 during a read, plate line210 and word line 110-a may be biased by an external voltage. In somecases, digit line 115-a is isolated from a virtually ground prior toapplying the external voltage to plate line 210 and word line 110-a.Selecting ferroelectric memory cell 105-a may result in a voltagedifference (e.g., plate line 210 voltage minus digit line 115-a voltage)across capacitor 205. The applied voltage difference may yield a changein the stored charge on capacitor 205, which may depend on the initialstate of capacitor 205—e.g., whether the initial state stored a logic“1” or a logic “0”—and may induce a voltage on digit line 115-a based onthe resulting charge stored on capacitor 205. The induced voltage ondigit line 115-a may then be compared to a reference (e.g., a voltage ofreference line 225) by sense component 125-a in order to determine thestored logic state in memory cell 105-a.

The specific sensing scheme or process may take many forms. In oneexample, digit line 115-a may have an intrinsic capacitance and developa non-zero voltage as capacitor 205 charges or discharges in response tothe voltage applied to plate line 210. The intrinsic capacitance maydepend on physical characteristics, including the dimensions, of digitline 115-a. Digit line 115-a may connect many memory cells 105 so digitline 115-a may have a length that results in a non-negligiblecapacitance (e.g., on the order of pico farads (pF)). The subsequentvoltage of digit line 115-a may depend on the initial logic state ofcapacitor 205, and sense component 125-a may compare this voltage to avoltage on reference line 225 provided by a reference component. Othersensing processes that take advantage of this change in charge may alsobe used.

With regard to a sensing scheme that utilizes the induced voltage ofdigit line 115-a, additional factors may negatively affect the sensingoperation—e.g., reduce the sensing window. As discussed above, a sensingwindow may be defined as the difference between the voltages that resulton digit line 115-a based at least in part on the initial state storedby ferroelectric capacitor 205. Factors such as ferroelectric memorycell characteristics, environmental characteristics, digit linecharacteristics, reference voltage errors, parasitic effects, and thelike, may reduce the sensing window associated with a memory cell 105-a.

By way of example, applying an external voltage to plate line 210 mayinduce a voltage on digit line 115-a due to parasitic elements inherentin a memory device. This induced voltage may effectively reduce theamount of charged that is shared with, or released to, the digit line115-a by ferroelectric capacitor 205 for both logic states. Accordingly,the resulting voltages for different logic states may be decreased,along with the difference between the resulting voltages. This decreasein the difference between the resulting voltages may thus decrease thesensing window. So a sensing scheme that maintains digit line 115-a ator near a ground reference while a voltage is applied to plate line 210may be utilized to mitigate sense margin loss (i.e., decrease in thesense window) by increasing the amount of charge that is released ontodigit line 115-a after selecting memory cell 105-a.

To write memory cell 105-a, a voltage may be applied across capacitor205. Various methods may be used. In one example, selection component220 may be activated through word line 110-a in order to electricallyconnect capacitor 205 to digit line 115-a. A voltage may be appliedacross capacitor 205 by controlling the voltage of cell plate 230 usingplate line 210 and controlling the voltage of cell bottom 215 usingdigit line 115-a. To write a logic “0,” cell plate 230 may be takenhigh, that is, a positive voltage may be applied to plate line 210, andcell bottom 215 may be taken low—e.g., virtually grounded using digitline 115-a. The opposite process is performed to write a logic “1”,i.e., cell plate 230 may be taken low and cell bottom 215 may be takenhigh. Read and write operations of capacitor 205 may account for thenon-linear properties associated with a ferroelectric device.

FIG. 3 illustrates examples of such non-linear properties withhysteresis curves 300-a (FIG. 3A) and 300-b (FIG. 3B) for a memory cellthat supports a sensing scheme for a ferroelectric memory cell inaccordance with various embodiments of the present disclosure.Hysteresis curves 300-a and 300-b illustrate an example ferroelectricmemory cell writing and reading process, respectively. Hysteresis curves300 depict the charge, Q, stored on a ferroelectric capacitor (e.g.,capacitor 205 of FIG. 2) as a function of a voltage, V.

A ferroelectric material is characterized by a spontaneous electricpolarization, i.e., it maintains a non-zero electric polarization in theabsence of an electric field. Example ferroelectric materials includebarium titanate (BaTiO₃), lead titanate (PbTiO₃), lead zirconiumtitanate (PZT), and strontium bismuth tantalate (SBT). The ferroelectriccapacitors described herein may include these or other ferroelectricmaterials. Electric polarization within a ferroelectric capacitorresults in a net charge at the ferroelectric material's surface andattracts opposite charge through the capacitor terminals. Thus, chargeis stored at the interface of the ferroelectric material and thecapacitor terminals. Because the electric polarization may be maintainedin the absence of an externally applied electric field for relativelylong times, even indefinitely, charge leakage may be significantlydecreased as compared with, for example, capacitors employed in DRAMarrays. This may reduce the need to perform refresh operations asdescribed above for some DRAM architectures.

Hysteresis curves 300 may be understood from the perspective of a singleterminal of a capacitor. By way of example, if the ferroelectricmaterial has a negative polarization, positive charge will accumulate atthe terminal. Likewise, if the ferroelectric material has a positivepolarization, negative charge will accumulate at the terminal.Additionally, it should be understood that the voltages in hysteresiscurves 300 represent a voltage difference across the capacitor and aredirectional. For example, a positive voltage may be applied by applyinga positive voltage to the terminal in question and maintaining thesecond terminal at ground. A negative voltage may be applied bymaintaining the terminal in question at ground and applying a positivevoltage to the second terminal—i.e., positive voltages may be applied tonegatively polarize the terminal in question. Similarly, two positivevoltages, two negative voltages, or any combination of positive andnegative voltages may be applied to the appropriate capacitor terminalsto generate the voltage difference shown in hysteresis curves 300.

As depicted in hysteresis curve 300-a, the ferroelectric material maymaintain a positive or negative polarization with a zero voltagedifference, resulting in two possible charged states: charge state 305and charge state 310. According to the example of FIG. 3, charge state305 represents a logic “0” and charge state 310 represents a logic “1.”In some examples, the logic values of the respective charge states maybe reversed to accommodate other schemes for operating a memory cell.

A logic “0” or “1” may be written to the memory cell by controlling theelectric polarization of the ferroelectric material, and thus the chargeon the capacitor terminals, by applying voltage. For example, applying anet positive voltage 315 across the capacitor results in chargeaccumulation until charge state 305-a is reached. Upon removing voltage315, charge state 305-a follows path 320 until it reaches charge state305 at zero voltage potential. Similarly, charge state 310 is written byapplying a net negative voltage 325, which results in charge state310-a. After removing negative voltage 325, charge state 310-a followspath 330 until it reaches charge state 310 at zero voltage.

To read, or sense, the stored state of the ferroelectric capacitor, avoltage may be applied across the capacitor. In response, the storedcharge changes, and the degree of the change depends on the initialcharge state—i.e., the degree to which the stored charge of thecapacitor changes varies depending on whether charge state 305-b or310-b was initially stored. For example, hysteresis curve 300-billustrates two possible stored charge states 305-b and 310-b. Netvoltage 335 may be applied to the cell plate (e.g., cell plate 230 withreference to FIG. 2) of the capacitor. Although depicted as a positivevoltage, voltage 335 may be negative. In response to voltage 335, chargestate 305-b may follow path 340. Likewise, if charge state 310-b wasinitially stored, then it follows path 345. The final position of chargestate 305-c and charge state 310-c depend on a number of factors,including the specific sensing operation and circuitry.

In some cases, the final charge may depend on the intrinsic capacitanceof the digit line of a memory cell. For example, if the capacitor iselectrically connected to the digit line and voltage 335 is applied, thevoltage of the digit line may rise due to its intrinsic capacitance, andthe voltage measured at a sense component may depend on the resultingvoltage of the digit line. The position of final charge states 305-c and310-c on hysteresis curve 300-b may thus depend on the capacitance ofthe digit line and may be determined through a load-line analysis—i.e.,charge states 305-c and 310-c may be defined with respect to the digitline capacitance. As a result, the voltage of the capacitor, voltage 350or voltage 355, may be different and may depend on the initial state ofthe capacitor.

By comparing the difference of the voltage applied to the cell plate(e.g., voltage 335) and the voltage across the capacitor (e.g., voltage350 or voltage 355) to a reference voltage, the initial state of thecapacitor may be determined. As can be understood by reference to FIG.2, the voltage of the digit line may be represented as the difference ofthe voltage applied to plate line 210 and the resulting voltage acrossthe capacitor 205. As discussed above, the voltage of the digit line isbased at least in part on the change in charge stored at the capacitor,and the change in charge is associated with the magnitude of the voltagethat is applied across the capacitor. In some examples, the referencevoltage may be an average of the digit line voltages that result fromvoltages 350 and 355 and, upon comparison, the sensed digit line voltagemay be determined to be higher or lower than the reference voltage. Avalue of the ferroelectric cell (i.e., a logic “0” or “1”) may then bedetermined based on the comparison.

A digit line that has an induced voltage as a result of parasiticeffects may reduce the magnitude of the voltage that is applied acrossthe capacitor, and therefore, decrease the resulting voltages 350 and355. As can be seen from hysteresis curves 300-a and 300-b, a decreasein the applied voltage may not yield proportional decreases in voltages350 and 355, and the sensing window—e.g., the difference between thedigit line voltages that result from voltages 350 and 355,respectively—may also be decreased. Therefore, a sensing scheme thatmaintains a digit line at or near a ground reference while a voltage isapplied to a plate of the capacitor may be utilized to mitigate sensemargin loss by increasing the voltage 335 that is applied across thecapacitor and the amount of charge that is shared with the digit line.

As discussed above, reading a memory cell that does not use aferroelectric capacitor may degrade or destroy the stored logic state. Aferroelectric memory cell, however, may maintain the initial logic stateafter a read operation. For example, if charge state 305-b is stored andthe read operation performed, the charge state may follow path 340 tocharge state 305-c, and after removing voltage 335, the charge state mayreturn to initial charge state 305-b, for example, by following path 340in the opposite direction.

FIG. 4 illustrates an example circuit 400 that supports a sensing schemefor a ferroelectric memory cell in accordance with various embodimentsof the present disclosure. Circuit 400 includes ferroelectric memorycell 105-b, word line 110-b (which may also be referred to as accessline 110-b), digit line 115-b, and sense component 125-b, which may beexamples of a ferroelectric memory cell 105, word line 110, digit line115, and sense component 125, respectively, as described with referenceto FIGS. 1 and 2. Circuit 400 may also include plate line 210-a andreference line 225-a, which may be examples of plate line 210 andreference line 225, respectively, as described with reference to FIG. 2.Additionally, according to the example of FIG. 4, digit line 115-b andreference line 225-a include intrinsic capacitance 415-a and intrinsiccapacitance 415-b, respectively. Circuit 400 also includes voltagesource 405, voltage source 410, switching component 420, and virtualground 425, parasitic capacitance 430.

Digit line 115-b and reference line 225-a may have respective intrinsiccapacitances 415-a and 415-b, respectively. Intrinsic capacitances 415-aand 415-b may not be electrical devices—i.e., may not be two-terminalcapacitors. Instead, intrinsic capacitances 415-a and 415-b may dependon physical characteristics, including the dimensions, of digit line115-b and reference line 225-a. In some cases, reference line 225-a isimplemented as an unused or inactive digit line of a memory array. Digitline 115-b may be connected to virtual ground 425 via switchingcomponent 420. Virtual ground 425 may act as a common reference forcircuit 400 and may also be referred to as ground or associated with azero voltage, although, the virtual ground may float to a voltage thatis different than (e.g., greater or less than) zero volts whenreferenced to an earth ground.

The voltage of reference line 225-a may be input to sense component125-b as a reference for comparison against the voltage of digit line115-b. A voltage may be applied to reference line 225-a to provide thereference for comparing with the voltage of digit line 115-b. Asdepicted, ferroelectric memory cell 105-b is in electronic communicationwith digit line 115-b. Ferroelectric memory cell 105-b may include aselection component in electronic communication with a ferroelectriccapacitor via word line 110-b, as described with reference to FIG. 2.The selection component may be activated by applying a voltage to wordline 110-b and may be used to provide a conductive path between theferroelectric capacitor and the digit line 115-b. In one example,ferroelectric memory cell 105-b may be selected, using the selectioncomponent, for a read operation to determine a state stored by theferroelectric capacitor.

Plate line 210-a may also be in electronic communication with theferroelectric capacitor. In some cases, a voltage may be applied to biasa plate of the ferroelectric capacitor via plate line 210-a (e.g., for aread operation). As mentioned above, applying the voltage to the plateline 210-a may induce parasitic voltages in other circuit locations. Forinstance, plate line 210-a may be capacitively coupled with digit line115-b via parasitic capacitance 430, and a change in the voltage appliedto plate line 210-a may also induce a change in the voltage applied todigit line 115-b. In some cases, plate line 210-a may be coupled withdigit line 115-b via other parasitic elements (e.g., inductance,resistance, etc.). These parasitic effects may reduce a resultingsensing window used to determine the state stored by the ferroelectriccapacitor. Applying the voltage to plate line 210-a in combination withapplying a voltage to word line 110-b may result in the ferroelectriccapacitor charging digit line 115-b. That is, upon accessingferroelectric memory cell 105-b, the ferroelectric capacitor may sharecharge with digit line 115-b via intrinsic capacitance 415-a.

According to the example of FIG. 4, switching component 420 is inelectronic communication with digit line 115-b and a ground reference.In some cases, switching component 420 may be used to connect or isolatedigit line 115-b to or from a virtual ground reference. In one example,a control signal (e.g., a linear equalization signal) may be used toactivate or deactivate switching component 420 by increasing ordecreasing a linear equalization voltage applied to the switchingcomponent, respectively. In some cases, switching component 420 may beused to prevent the voltage of digit line 115-b from floating whiledigit line 115-b is not being used. Switching component 420 may also beused to combat the parasitic effects associated with applying a voltageto plate line 210-a. For instance, switching component 420 may bemaintained in an active state while the voltage is applied to plate lineto dampen a parasitic voltage induced on digit line 115-b and to drivethe voltage of digit line 115-b to or near virtual ground 425, as willbe described in more detail below.

In some examples, switching component 420 is referred to as a linearequalization device. Switching component 420 may be implemented as atransistor (e.g., an n or p-type FET) and may be activated/deactivatedby applying increasing or reducing a control signal, or an amplifiedversion of the control signal, to a gate of the transistor. In somecases, a voltage may be applied to plate line 210-a, word line 110-a,reference line 225-a, voltage source 405, or voltage source 410 viaexternal/internal voltage source(s), amplifier(s), or line driver(s).

Sense component 125-b may be used to determine the stored state offerroelectric memory cell 105-b. In some cases, sense component 125-b isor includes a sense amplifier. Sense component 125-b may be operated byvoltage source 405 and voltage source 410. In some examples, voltagesource 405 is a positive supply voltage, while voltage source 410 is anegative supply voltage or a virtual ground. Sense component 125-b maybe used to determine a logic value of the ferroelectric memory cell105-b based at least in part on the voltage of digit line 115-b and thevoltage of the reference line 225-a. Sense component 125-b may beactivated or deactivated by a controller. In some examples, sensecomponent 125-b is activated or “fired” to trigger a comparison betweenthe voltage of digit line 115-b and the voltage of reference line 225-a.Triggering sense component 125-b may include activating switchingcomponents that are in electronic communication with respective voltagesources 405 and 410 and sense component 125-b.

Sense component 125-b may latch the output of a sense amplifier to thevoltage provided by either voltage source 405 or voltage source 410. Forinstance, if the voltage of the digit line 115-b is greater than thevoltage of the reference line 225-a, then sense component 125-b maylatch the output of the sense amplifier at a positive voltage suppliedfrom voltage source 405. Reducing the parasitic effects on digit line115-b may increase the sensing window for sensing operations, mitigatingmargin losses and increasing the reliability for reading memory cell105-b.

FIG. 5 illustrates a timing diagram 500 for a sensing scheme for aferroelectric memory cell in accordance with various embodiments of thepresent disclosure. Timing diagram 500 depicts voltage on axis 505 andtime on axis 510. The voltage of various components as a function oftime may thus be represented on timing diagram 500. For example, timingdiagram 500 includes word line voltage 515, plate line voltage 520, anddigit line voltages 530-a and 530-b. Timing diagram 500 may also includeread voltage 535, reference voltage 540, duration 545, sensing window550, active duration 555, and firing time 560. Timing diagram 500depicts an example operation of circuit 400 described with reference toFIG. 4. FIG. 5 is described below with reference to components ofpreceding figures. Voltages that approach zero may be offset from axis510 for ease of representation; in some cases, these voltages may beequal to or approximately equal to zero.

As discussed with reference to FIG. 4, a voltage may be applied toswitching component 420 to virtually ground digit line 115-b. In theexample depicted in FIG. 5, a subsequent voltage may be applied to plateline 210-a. A read voltage—i.e., the voltage used to read the state of aferroelectric capacitor—may be applied to plate line 210-a, biasing theferroelectric capacitor. The plate line voltage 520, which may bemeasured at the plate of the ferroelectric capacitor, may increase withthe applied read voltage. The change in plate line voltage 520 may causea change in the digit line voltage 530 due, in part, to the parasiticelements of the digit line. As discussed above, this increase in thedigit line voltage 530 may decrease the amount of charged shared withdigit line 115-b from the ferroelectric capacitor and, in turn, maydecrease sensing window 550—e.g., the difference between digit linevoltage 530-a and 530-b. Therefore, the linear equalization voltage 525may be applied and maintained at switching component 420 while applyingthe voltage to plate line 210-a. By maintaining switching component 420in an active state, the resulting parasitic voltage on digit line 115-bmay be dampened, and the digit line voltage 530 may be held near and/ordriven towards zero volts or virtual ground.

In some cases, switching component 420 may be maintained in an activestate until a threshold associated with applying the voltage is reached.For instance, switching component 420 may remain active until adetermination has been made that the magnitude of the voltage of plateline 210-a is greater than a threshold voltage, the rate of change ofthe voltage of the plate line 210-a is less than or within a thresholdvalue, or both. Additionally or alternatively, the threshold may beassociated with a duration (e.g., duration 545) following theapplication of plate line voltage 520 or the satisfying of a voltagethreshold. In some cases, the duration may be determined based at leastin part on the size of the resulting sensing window 550, acharacteristic of the ferroelectric capacitor (e.g., age, acorresponding hysteresis curve), environmental factors (e.g.,temperature), a characteristic of the digit line (trace width, tracelength, etc.), or any combination thereof. In some examples, anincreased duration may be associated with an increased sensing window550. Therefore, in one example, duration 545 may be increased for olderferroelectric memory arrays with ferroelectric capacitors that may beexperiencing degraded hysteresis characteristics.

In some examples, duration 545 may be shortened or lengthened toaccommodate different parasitic effects. For instance, duration 545 maybe set long enough to remove some or all of the parasitic voltage fromdigit line 115-b (e.g., when digit line voltage 530 is less than 0.5millivolts (mV)). In some cases, a duration 545 associated with removinga parasitic voltage or an increased sensing window 550, or both, may bedetermined using a mathematical model that has been developed for aferroelectric memory array or based on established testing results. Inother cases, duration 545 may be determined based on a timing associatedwith a reading or writing to ferroelectric memory cell 105-b. Forinstance, active duration 555 may be associated with a timing forreading ferroelectric memory cell 105-b and may include the time betweenraising and lowering the plate voltage. In some examples, duration 545may be shortened to reduce active duration 555 and to accommodate atiming used by a memory device to complete a read operation. In someexamples, duration 545 may be less than or equal to three nanoseconds (3ns).

After a threshold has been reached—e.g., a voltage threshold has beenreached, duration 545 has expired, or the like—linear equalizationvoltage 525 may be reduced (e.g., ramped down or dropped to 0V) todeactivate switching component 420. In some cases, linear equalizationvoltage 525 is reduced while plate line voltage 520 is increased. Afterdeactivating switching component 420, digit line 115-b may be isolatedfrom the virtual ground reference. Subsequently, a word line voltage 515may be applied at word line 110-b to access ferroelectric memory cell105-b. The word line voltage 515, which may be measured at the gate of aselection component, may increase with the applied access voltage. Insome cases, word line voltage 515 may increase while linear equalizationvoltage 525 decreases. As the word line voltage 515 increases, aconductive path between the charged ferroelectric capacitor and digitline 115-b may be provided through the selection component. Accordingly,the digit line voltage 530 may rise as the ferroelectric capacitordischarges onto digit line 115-b.

In the example depicted in FIG. 5, the digit line voltage 530 may riseto one of two voltages based on the stored state. Although, as discussedabove, these two voltages may vary based at least in part on theresidual parasitic effects on digit line 115-b. For instance, if a logic“1” is stored by the ferroelectric capacitor, then digit line voltage530-a may result, while digit line voltage 530-b may result if a logic“0” is stored. Digit line voltage 530-a may be associated with a smallervoltage drop over the ferroelectric cell and therefore a higher digitline voltage when compared with digit line voltage 530-b, as can be seenwith respect to FIG. 3. The sensing window 550 between digit linevoltage 530-a and digit line voltage 530-b may change based on the sizeof duration 545. In some examples, a longer duration 545 is associatedwith an increased sensing window 550 while a shorter duration 545 isassociated with a decreased sensing window 550. As mentioned above, thedetermined duration 545 may be selected based on a number of factors.

After digit line voltage 530-a or 530-b has settled, sense component125-b may be activated at firing time 560. The sense component 125-b maycompare the digit line voltage 530 with the reference voltage 540 andthe output of the sense component 125-b may be latched, accordingly. Forinstance, if a logic value “1” is stored by the ferroelectric capacitor,then the sense component 125-b may compare digit line voltage 530-a withreference voltage 540 and may determine the digit line voltage 530-a ishigher than the reference voltage 540. Therefore, the output of thesense component 125-b may be driven to a positive supply voltage andlatched. In the example depicted in FIG. 5, when the sense component125-b outputs the positive supply voltage, digit line 115-b is alsodriven to the supply voltage.

FIG. 6 illustrates a block diagram 600 of an example ferroelectricmemory array 100-a that supports a sensing scheme for a ferroelectricmemory cell in accordance with various embodiments of the presentdisclosure. Memory array 100-a may contain memory controller 140-a,memory cell 105-c, and virtual ground 425-a, which may be examples ofmemory controller 140, memory cell 105, and virtual ground 425 describedwith reference to FIG. 1, 2, or 4.

Memory controller 140-a may include biasing component 610, timingcomponent 615, and linear equalization component 630 and may operatememory array 100-a as described in FIGS. 1-5. Memory controller 140-amay be in electronic communication with word line 110-c, digit line115-c, sense component 125-c, and plate line 210-a, and switchingcomponent 420-a, which may be examples of word line 110, digit line 115,sense component 125, plate line 210, and switching component 420described with reference to FIG. 1, 2, or 4.

Memory array 100-a may also include reference component 620, latch 625,equalization line 635, and virtual ground 425-a. The components ofmemory array 100-a may be in electronic communication with one anotherand may perform the functions described with reference to FIGS. 1-5. Insome cases, reference component 620, sense component 125-c, switchingcomponent 420-a, and latch 625 are components of memory controller140-a.

In some examples, digit line 115-c is in electronic communication withswitching component 420-a, sense component 125-c, and a ferroelectriccapacitor of ferroelectric memory cell 105-c. Word line 110-c may be inelectronic communication with memory controller 140-a and a selectioncomponent of memory cell 105-c. Plate line 210-a may be in electroniccommunication with memory controller 140-a and a plate of aferroelectric capacitor of ferroelectric memory cell 105-c. Sensecomponent 125-c may be in electronic communication with memorycontroller 140-a, reference line 225-b, digit line 115-c, and latch 625.Reference component 620 may be in electronic communication with memorycontroller 140-a and reference line 225-b. Switching component 420-a maybe in electronic communication with memory controller 140-a, digit line115-c, and virtual ground 425-a. These components may also be inelectronic communication with other components, both inside and outsideof memory array 100-a, not listed above, via other components,connections, or busses.

Memory controller 140-a may be configured to activate word line 110-c,plate line 210-a, digit line 115-c, or equalization line 635 by applyingvoltages to those various nodes. For example, biasing component 610 maybe configured to apply a voltage to operate memory cell 105-c to read orwrite memory cell 105-c as described above. In some cases, memorycontroller 140-a may include a row decoder, column decoder, or both, asdescribed with reference to FIG. 1. This may enable memory controller140-a to access one or more memory cells 105. Biasing component 610 mayalso provide voltage potentials to reference component 620 in order togenerate a reference signal for sense component 125-c. Additionally,biasing component 610 may provide signals or apply voltages for theoperation of sense component 125-c.

In some cases, memory controller 140-a may perform its operations usingtiming component 615. For example, timing component 615 may control thetiming of the various word line selections or plate biasing, includingtiming for switching and voltage application to perform the memoryfunctions, such as reading and writing, discussed herein. In some cases,timing component 615 may control the operations of biasing component610.

Reference component 620 may include various components to generate areference signal for sense component 125-c. Reference component 620 mayinclude circuitry specifically configured to produce a reference signal.In some cases, reference component 620 includes another ferroelectricmemory cell 105. In some examples, reference component 620 may beconfigured to output a voltage with a value between the two sensevoltages, as described with reference to FIG. 3. Or reference component620 may be designed to output a virtual ground voltage (i.e.,approximately 0V). Sense component 125-c may compare a signal frommemory cell 105-c (through digit line 115-c) with a reference signalfrom reference component 620. Upon determining the logic state, sensecomponent 125-c may then store the output in latch 625, where it may beused in accordance with the operations of an electronic device using thememory device of which memory array 100-a is a part.

In some cases, memory controller 140-a may use equalization line 635 tovirtually ground digit line 115-c while a voltage is applied to plateline 210-a. For example, switching component 420-a may be used tovirtually ground digit line 115-c with virtual ground 425-a; biasingcomponent 610 may be used to apply a voltage to a plate of theferroelectric capacitor via plate line 210-a while digit line 115-c isvirtually grounded; and switching component 420-a may be used to isolatedigit line 115-c from virtual ground 425-a after applying the voltage tothe plate of the ferroelectric capacitor and after a thresholdassociated with applying the voltage is reached.

In some examples, memory controller 140-a may use biasing component 610to activate and deactivate switching component 420-a via equalizationline 635. In some cases, memory controller 140-a may use linearequalization component 630, which may be in electronic communicationwith switching component 420-a. Linear equalization component 630 mayuse biasing component 610 to adjust a linear equalization voltageapplied to equalization line 635, which, in some cases, may activateswitching component 420-a and virtually ground digit line 115-c.

In some cases, memory controller 140-a may use biasing component 610 toactivate a selection component that is in electronic communication withthe ferroelectric capacitor for a sense operation of ferroelectricmemory cell 105-c and may determine a timing of the sense operationbased at least in part on the applied linear equalization voltage. Insome cases, memory controller 140-a activates the selection component byusing biasing component 610 to apply a voltage to a word line 110-c.Memory controller 140-a may use timing component 615 to determine aduration between applying the voltage to the ferroelectric capacitor andisolating the digit line.

FIG. 7 illustrates a system 700 that supports a sensing scheme for aferroelectric memory cell in accordance with various embodiments of thepresent disclosure. System 700 includes a device 705, which may be orinclude a printed circuit board to connect or physically support variouscomponents. Device 705 includes a memory array 100-b, which may be anexample of memory array 100 described with reference to FIG. 1 and FIG.6. Memory array 100-b may contain memory controller 140-b and memorycell(s) 105-d, which may be examples of memory controller 140 describedwith reference to FIGS. 1 and 6 and memory cells 105 described withreference to FIG. 1-6. Device 705 may also include a processor 710, BIOScomponent 715, peripheral component(s) 720, and input/output controlcomponent 725. The components of device 705 may be in electroniccommunication with one another through bus 730.

Processor 710 may be configured to operate memory array 100-a throughmemory controller 140-b. In some cases, processor 710 may perform thefunctions of memory controller 140 described with reference to FIGS. 1and 6. In other cases, memory controller 140-b may be integrated intoprocessor 710. Processor 710 may be a general-purpose processor, adigital signal processor (DSP), an application-specific integratedcircuit (ASIC), a field-programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or it may be a combination of these types ofcomponents, and processor 710 may perform various functions describedherein, including supporting a sensing scheme for a memory cell.Processor 710 may, for example, be configured to executecomputer-readable instructions stored in memory array 100-a to causedevice 705 perform various functions or tasks.

BIOS component 715 may be a software component that includes a basicinput/output system (BIOS) operated as firmware, which may initializeand run various hardware components of system 700. BIOS component 715may also manage data flow between processor 710 and the variouscomponents, such as peripheral components 720, input/output controlcomponent 725, etc. BIOS component 715 may include a program or softwarestored in read-only memory (ROM), flash memory, or any othernon-volatile memory.

Peripheral component(s) 720 may be any input or output device, or aninterface for such devices, that is integrated into device 705. Examplesmay include disk controllers, sound controller, graphics controller,Ethernet controller, modem, USB controller, a serial or parallel port,or peripheral card slots, such as peripheral component interconnect(PCI) or accelerated graphics port (AGP) slots.

Input/output control component 725 may manage data communication betweenprocessor 710 and peripheral component(s) 720, input devices 735, oroutput devices 740. Input/output control component 725 may also manageperipherals not integrated into device 705. In some cases, input/outputcontrol component 725 may represent a physical connection or port to theexternal peripheral.

Input 735 may represent a device or signal external to device 705 thatprovides input to device 705 or its components. This may include a userinterface or interface with or between other devices. In some cases,input 735 may be a peripheral that interfaces with device 705 viaperipheral component(s) 720 or may be managed by input/output controlcomponent 725.

Output device 740 may represent a device or signal external to device705 configured to receive output from device 705 or any of itscomponents. Examples of output device 740 may include a display, audiospeakers, a printing device, another processor or printed circuit board,etc. In some cases, output 740 may be a peripheral that interfaces withdevice 705 via peripheral component(s) 720 or may be managed byinput/output control component 725.

The components of memory controller 140-b, device 705, and memory array100-b may be made up of circuitry designed to carry out their functions.This may include various circuit elements, for example, conductivelines, transistors, capacitors, inductors, resistors, amplifiers, orother active or inactive elements, configured to carry out the functionsdescribed herein.

FIG. 8 is a flowchart that illustrates a method 800 or methods for asensing scheme for a ferroelectric memory cell in accordance withvarious embodiments of the present disclosure. The operations of method800 may be implemented by a memory array 100, as described withreference to FIGS. 1-7. For example, the operations of method 800 may beperformed by a memory controller 140, as described with reference toFIGS. 1, 6, and 7. In some examples, a memory controller 140 may executea set of codes to control the functional elements of the memory array100 to perform the functions described below. Additionally oralternatively, the memory controller 140 may perform features thefunctions described below using special-purpose hardware.

At block 805, the method 800 may include virtually grounding a digitline that is in electronic communication with a ferroelectric capacitorof the ferroelectric memory cell and a virtual ground. In certainexamples, the operations of block 805 may be performed or facilitated bythe switching component 420-a, as described with reference to FIG. 6. Insome cases, virtually grounding the digit line may include activating aswitching component that is in electronic communication with the digitline and the virtual ground. Activating the switching component mayinclude applying a linear equalization voltage to the switchingcomponent.

At block 810, the method 800 may include applying a voltage to a plateof the ferroelectric capacitor while the digit line is virtuallygrounded. In certain examples, the operations of block 810 may beperformed or facilitated by the biasing component 610, as described withreference to FIG. 6. Applying the voltage to the plate of theferroelectric capacitor may include ramping a voltage applied to theplate of the ferroelectric capacitor. In one example, the voltageapplied to the plate of the ferroelectric capacitor is ramped from zerovolts to a fraction of a source voltage for an array, where theferroelectric memory cell may be a portion of the array. In some cases,the voltage applied to the plate is increased while the linearequalization voltage is reduced.

At block 815, the method 800 may include isolating the digit line fromthe virtual ground after applying the voltage to the plate of theferroelectric capacitor and after a threshold associated with applyingthe voltage is reached. In certain examples, the operations of block 815may be performed or facilitated by the switching component 420-a, asdescribed with reference to FIG. 6. In some cases, isolating the digitline from the virtual ground may include deactivating the switchingcomponent. Deactivating the switching component may include reducing alinear equalization voltage applied to the switching component that isin electronic communication with the digit line and the virtual ground.

In some cases, the method 800 may include determining the threshold hasbeen reached, wherein the threshold is associated with at least one of amagnitude of a voltage of the plate or a rate of change of the voltageof the plate, or both. The threshold may be associated with a durationfollowing the voltage application to the plate of the ferroelectriccapacitor, and the duration may be determined based at least in part ona timing associated with reading or writing to the ferroelectric memorycell or a removing a parasitic voltage from the digit line, or both. Forinstance, the duration may be less than or equal to 3 ns. In someexamples, the method 800 may include activating a selection componentthat is in electronic communication with the ferroelectric capacitor fora sense operation of the ferroelectric memory cell after the linearequalization voltage is reduced. Activating the selection component mayinclude applying a voltage to a word line in electronic communicationwith the ferroelectric memory cell. In some cases, the voltage appliedto the word line is increased while the linear equalization voltage isreduced.

FIG. 9 is a flowchart that illustrates a method 900 or methods for asensing scheme for a ferroelectric memory cell in accordance withvarious embodiments of the present disclosure. The operations of method900 may be implemented by a memory array 100, as described withreference to FIGS. 1-7. For example, the operations of method 900 may beperformed by a memory controller 140, as described with reference toFIGS. 1, 6, and 7. In some examples, a memory controller 140 may executea set of codes to control the functional elements of the memory array100 to perform the functions described below. Additionally oralternatively, the memory controller 140 may perform features thefunctions described below using special-purpose hardware.

At block 905, the method 900 may include activating a switchingcomponent that is in electronic communication with a digit line and avirtual ground. In certain examples, the operations of block 905 may beperformed or facilitated by the biasing component 610, as described withreference to FIG. 6. Activating the switching component may includeapplying a voltage to the switching component.

At block 910, the method 900 may include applying a voltage to aferroelectric capacitor of the ferroelectric memory cell that is inelectrical communication with the digit line, wherein the voltage isapplied for a sensing operation. In certain examples, the operations ofblock 910 may be performed or facilitated by the biasing component 610,as described with reference to FIG. 6.

At block 915, the method 900 may include deactivating the switchingcomponent after applying the voltage to the ferroelectric capacitor. Incertain examples, the operations of block 915 may be performed orfacilitated by the biasing component 610 and/or timing component 615, asdescribed with reference to FIG. 6. Deactivating the switching componentmay include removing the voltage. In some cases, the switching componentis deactivated based at least in part on determining a magnitude of avoltage of a plate of the ferroelectric capacitor has reached a firstthreshold or determining a rate of change for the voltage of the plateis within a second threshold, or both. In some cases, the method 900 mayinclude determining a duration between applying the voltage to theferroelectric capacitor and deactivating the switching component. Theduration may be determined based at least in part on: a characteristicof the ferroelectric memory cell, a characteristic of the digit line, atiming associated with reading or writing to the ferroelectric memorycell; a full dump window size, where the full dump window size may bedetermined based at least in part on a measured difference between avoltage of the digit line resulting from a first state stored by theferroelectric capacitor and a voltage of the digit line resulting from asecond stored state stored by the ferroelectric capacitor, or anycombination thereof.

At block 920, the method 900 may include selecting the ferroelectricmemory cell after deactivating the switching component. In certainexamples, the operations of block 915 may be performed or facilitated bythe biasing component 610 and/or timing component 615, as described withreference to FIG. 6. Selecting the ferroelectric memory cell may includeapplying a voltage to a selection component that is in electroniccommunication with the ferroelectric capacitor and the digit line.

Thus, methods 800 and 900 may provide for a sensing scheme for a memorycell for a ferroelectric memory array. Methods 800 and 900 may each bemethods of operating a ferroelectric memory cell. It should be notedthat methods 800 and 900 describe possible implementations, and theoperations and steps may be rearranged or otherwise modified such thatother implementations are possible. In some examples, features from twoor more of the methods 800 and 900 may be combined.

The description herein provides examples, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure.

Various examples may omit, substitute, or add various procedures orcomponents as appropriate. Also, features described with respect to someexamples may be combined in other examples.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The terms “example” and “exemplary,” as used herein, mean“serving as an example, instance, embodiment, or illustration,” and not“preferred” or “advantageous over other examples.” The detaileddescription includes specific details for the purpose of providing anunderstanding of the described techniques. These techniques, however,may be practiced without these specific details. In some instances,well-known structures and devices are shown in block diagram form inorder to avoid obscuring the concepts of the described examples.

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. When the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof. Some drawings may illustrate signals as a single signal;however, it will be understood by a person of ordinary skill in the artthat the signal may represent a bus of signals, where the bus may have avariety of bit widths.

As used herein, the term “virtual ground” refers to a node of anelectrical circuit that is held at a voltage of approximately zero volts(0V) but that is not directly connected with ground. Accordingly, thevoltage of a virtual ground may temporarily fluctuate and return toapproximately 0V at steady state. A virtual ground may be implementedusing various electronic circuit elements, such as a voltage dividerconsisting of operational amplifiers and resistors. Otherimplementations are also possible. “Virtual grounding” or “virtuallygrounded” means connected to approximately 0V.

The term “electronic communication” refers to a relationship betweencomponents that supports electron flow between the components. This mayinclude a direct connection between components or may includeintermediate components. Components in electronic communication may beactively exchanging electrons or signals (e.g., in an energized circuit)or may not be actively exchanging electrons or signals (e.g., in ade-energized circuit) but may be configured and operable to exchangeelectrons or signals upon a circuit being energized. By way of example,two components physically connected via a switch (e.g., a transistor)are in electronic communication regardless of the state of the switch(i.e., open or closed).

The term “isolated” refers to a relationship between components in whichelectrons are not presently capable of flowing between them; componentsare isolated from each other if there is an open circuit between them.For example, two components physically connected by a switch may beisolated from each other when the switch is open.

The devices discussed herein, including memory array 100, may be formedon a semiconductor substrate, such as silicon, germanium,silicon-germanium alloy, gallium arsenide, gallium nitride, etc. In somecases, the substrate is a semiconductor wafer. In other cases, thesubstrate may be a silicon-on-insulator (SOI) substrate, such assilicon-on-glass (SOG) or silicon-on-sapphire (SOP), or epitaxial layersof semiconductor materials on another substrate. The conductivity of thesubstrate, or sub-regions of the substrate, may be controlled throughdoping using various chemical species including, but not limited to,phosphorous, boron, or arsenic. Doping may be performed during theinitial formation or growth of the substrate, by ion-implantation, or byany other doping means.

A transistor or transistors discussed herein may represent afield-effect transistor (FET) and comprise a three terminal deviceincluding a source, drain, and gate. The terminals may be connected toother electronic elements through conductive materials (e.g., metals).The source and drain may be conductive and may comprise a heavily-doped(e.g., degenerate), semiconductor region. The source and drain may beseparated by a lightly-doped semiconductor region or channel. If thechannel is n-type (i.e., majority carriers are electrons), then the FETmay be referred to as a n-type FET. If the channel is p-type (i.e.,majority carriers are holes), then the FET may be referred to as ap-type FET. The channel may be capped by an insulating gate oxide. Thechannel conductivity may be controlled by applying a voltage to thegate. For example, applying a positive voltage or negative voltage to ann-type FET or a p-type FET, respectively, may result in the channelbecoming conductive. A transistor may be “on” or “activated” when avoltage greater than or equal to the transistor's threshold voltage isapplied to the transistor gate. The transistor may be “off” or“deactivated” when a voltage less than the transistor's thresholdvoltage is applied to the transistor gate.

The various illustrative blocks, components, and modules described inconnection with the disclosure herein may be implemented or performedwith a general-purpose processor, a DSP, an ASIC, an FPGA or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general-purpose processor may be amicroprocessor, but in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computing devices(e.g., a combination of a DSP and a microprocessor, multiplemicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations. Also, as used herein, including in the claims, “or” as usedin a list of items (for example, a list of items prefaced by a phrasesuch as “at least one of” or “one or more of”) indicates an inclusivelist such that, for example, a list of at least one of A, B, or C meansA or B or C or AB or AC or BC or ABC (i.e., A and B and C).

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media cancomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such asinfrared, radio, and microwave, then the coaxial cable, fiber opticcable, twisted pair, digital subscriber line (DSL), or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. Disk and disc, as used herein, include CD, laserdisc, optical disc, digital versatile disc (DVD), floppy disk andBlu-ray disc where disks usually reproduce data magnetically, whilediscs reproduce data optically with lasers. Combinations of the aboveare also included within the scope of computer-readable media.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notto be limited to the examples and designs described herein but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method, comprising: coupling a first accessline with a ground node, wherein the first access line is coupled with acapacitor of a memory cell; applying a voltage to a second access linecoupled with the capacitor; and isolating the first access line from theground node after applying the voltage to the second access line coupledwith the capacitor.
 2. The method of claim 1, further comprising:determining that a threshold associated with applying the voltage issatisfied; and sensing a logic state of the memory cell as part of aread operation based at least in part on determining that the thresholdassociated with applying the voltage is satisfied.
 3. The method ofclaim 2, further comprising: identifying a magnitude of the voltage ofthe second access line and a threshold voltage; and determining that thethreshold associated with applying the voltage has been satisfied basedat least in part on the magnitude of the voltage of the second accessline being greater than or equal to the threshold voltage.
 4. The methodof claim 2, wherein sensing the logic state of the memory cellcomprises: determining a voltage of the first access line based at leastin part on isolating the first access line from the ground node;comparing the voltage of the first access line to a voltage of areference line; and determining the logic state of the memory cell basedat least in part on the comparing.
 5. The method of claim 4, furthercomprising: activating a sense component to initiate comparing thevoltage of the first access line to the voltage of the reference line.6. The method of claim 2, further comprising: determining a durationsince applying the voltage to the second access line of the capacitor;and determining that the threshold has been satisfied based at least inpart on the duration.
 7. The method of claim 6, further comprising:determining the duration based at least in part on a timing associatedwith reading the memory cell, or writing to the memory cell, or removingthe voltage from the second access line, or any combination thereof. 8.The method of claim 1, wherein isolating the first access linecomprises: reducing a voltage applied to a switching component coupledwith the first access line and the ground node based at least in part onapplying the voltage to the second access line.
 9. The method of claim1, further comprising: applying a voltage to a third access line coupledwith the memory cell, wherein the voltage applied to the third accessline activates a selection component.
 10. The method of claim 1, whereinthe first access line comprises a digit line and the second access linecomprises a plate line.
 11. An apparatus, comprising: an array of memorycells; and a controller coupled with the array of memory cells andoperable to cause the apparatus to: couple a first access line with aground node, wherein the first access line is coupled with a capacitorof a memory cell; apply a voltage to a second access line coupled withthe capacitor; and isolate the first access line from the ground nodeafter applying the voltage to the second access line coupled with thecapacitor.
 12. The apparatus of claim 11, wherein the controller isfurther operable to cause the apparatus to: determine that a thresholdassociated with applying the voltage is satisfied; and sense a logicstate of the memory cell as part of a read operation based at least inpart on determining that the threshold associated with applying thevoltage is satisfied.
 13. The apparatus of claim 12, wherein thecontroller is further operable to cause the apparatus to: identify amagnitude of the voltage of the second access line and a thresholdvoltage; and determine that the threshold associated with applying thevoltage has been satisfied based at least in part on the magnitude ofthe voltage of the second access line being greater than or equal to thethreshold voltage.
 14. The apparatus of claim 12, wherein the controlleris further operable to cause the apparatus to: determine a durationsince applying the voltage to the second access line of the capacitor;and determine that the threshold has been satisfied based at least inpart on duration.
 15. The apparatus of claim 14, wherein the controlleris further operable to cause the apparatus to: determine the durationbased at least in part on a timing associated with reading the memorycell, or writing to the memory cell, or removing the voltage from thesecond access line, or any combination thereof.
 16. The apparatus ofclaim 11, wherein isolating the first access line comprises: reduce avoltage applied to a switching component coupled with the first accessline and the ground node based at least in part on applying the voltageto the second access line.
 17. The apparatus of claim 11, wherein thecontroller is further operable to cause the apparatus to: apply avoltage to a third access line coupled with the memory cell, wherein thevoltage applied to the third access line activates a selectioncomponent.
 18. An apparatus, comprising: a first access line coupledwith a capacitor of a memory cell; a second access line coupled with thecapacitor; a switching component configured to couple the first accessline with a ground node; and a voltage source configured to apply avoltage to the second access line, wherein the switching component isfurther configured to isolate the first access line from the ground nodeafter applying the voltage to the second access line.
 19. The apparatusof claim 18, further comprising: a sense component configured to sense alogic state of the memory cell as part of a read operation based atleast in part on applying the voltage to the second access line.
 20. Theapparatus of claim 18, further comprising: a second voltage sourceconfigured to apply a voltage to a third access line coupled with thememory cell, wherein the voltage applied to the third access lineactivates a selection component.